Influence of point defects injection on the stability of a supersaturated Ga-Si solid solution

The ultrahigh doping levels of Si needed in ultradownscaled electronic devices can be achieved forming supersaturated solid solutions by solid-phase epitaxy. These solutions are, however, unstable upon high-temperature annealing, and electrical deactivation of the impurities exceeding the solid solubility limit occurs. There are indications that deactivation is driven by the interaction of impurities with native (i.e., intrinsic) defects, but the relevant process has not been studied in detail thus far, nor have the defect complexes presumably causing the deactivation been identified. Here we use light-ion beam treatments and Rutherford backscattering analysis combined with first-principles density-functional calculations to investigate the interaction of a specific Group-III acceptor, Ga, with native defects-mostly self-interstitials-generated by irradiation at room temperature, or upon thermal annealing. Monitoring the off-lattice displacement of Ga during He-beam irradiation at room temperature or after high-temperature annealing by channeling analysis, we find a partitioning into substitutional and tetrahedral interstitial Ga populations in the former case, and a partitioning into substitutional and random populations in the latter. Based on ab initio calculations and angular-scan Rutherford backscattering spectroscopy, we are able to interpret the results in terms of (a) self-interstitial-assisted enhanced diffusion of Ga, and (b) the subsequent formation of stable Ga-Ga and Ga-Ga-Si complexes. This suggests that deactivation is indeed mediated by native defects (mainly self-interstitials) causing the off-site displacement of the Ga impurity.